1. Field of Invention
The present invention relates to an electrostatic image-developing toner for use in developing with a developer electrostatic latent images formed by electrophotographic, electrostatic, or other recording method, a method for producing the same, and a dispersion of resin particles or condensation compound particles used as the raw material.
2. Description of the Related Art
Methods such as electrophotographic processes that visualize image information via electrostatic images are currently being used in a variety of fields. In such an electrophotographic process, image information is visualized by the steps of forming an electrostatic image on a photosensitive body by electrostatic charging or light exposure, developing the electrostatic latent image formed thereon with a developer containing a toner, and transferring and fixing the developed image. Both two-component developers, consisting of a toner and a carrier, and one-component developers, that employ only one magnetic or nonmagnetic toner are known as developers for use in such systems. Such toners are usually produced in a kneading-pulverizing process, comprising melt-blending a thermoplastic resin with a pigment, a charge-controlling agent, and a releasing agent such as a wax or the like, cooling the blend and pulverizing and classifying the cooled resin. Inorganic or organic microparticles are occasionally added to the toner if needed as an additive to the toner particle surface for improvement in fluidity and cleanability.
Recently, copying machines and printers using the color electrophotographic method, and multifunctional processing machines containing such devices as well as facsimile are becoming more and more popular. For obtaining a favorable glossiness of the images during reproduction of color images and a favorable transparency of OHP images, a great amount of oil is applied onto the fixing roll for facilitating release, because it is generally difficult to use a releasing agent such as wax. As a result, it becomes difficult to prevent a greasy feeling of the reproduced images, including those on OHP sheets, and to append additional characters or images on the image reproduced, for example, with a pen. In addition, the use of oil often results in uneven glossiness of images. It is difficult to use a wax such as polyethylene, polypropylene, or paraffin, which are commonly used for normal black-and-white copying, because they impair the transparency of the resulting OHP images.
When the conventional kneading pulverization process is used for producing a toner, not only does it result in problems such as deterioration in transparency but also a drastic deterioration in flowability and occurrence of filming on the developing machine, photosensitive body, and the like result when the toner is used as a developer, because of difficulty in controlling the amount of surface exposure of the releasing agent on the toner particle surface.
To overcome these problems thoroughly, proposed were processes for producing toners by polymerization, specifically, processes of forming a toner containing a wax capsulated inside and thereby controlling the exposure thereof on the surface, comprising dispersing an oil phase, containing a monomer of the base material for the resin and a colorant, in an aqueous phase and polymerizing the monomer directly into toner.
Further, methods of producing toners by an emulsion polymerization aggregation process were proposed in JP-A Nos. 63-282752 and 6-250439 as another means for systematically controlling of the shape and the surface structure of the toners. These documents teach general processes for producing toners, comprising producing a resin particle dispersion by emulsion polymerization or the like, producing a colorant dispersion containing a colorant dispersed in a solvent, mixing the resin particle dispersion and the colorant dispersion, forming aggregates corresponding to toner particles, and melt-coalescing the aggregates by heating.
These manufacturing processes not only allow capsulation of the wax in the toner particles, but also make easy a reduction of the toner particle diameter, and enable reproduction of sharper images higher in resolution.
As described above, for providing high-quality images in the electrophotography process and stabilized performance of the toner under various mechanical stresses, it is extremely important to optimize the kind and amount of the pigment and the releasing agent used, prevent exposure of the releasing agent on the particle surface, improve the glossiness of printed images by optimization of the resin properties and the releasing property without using a fixing oil, and control hot offsetting.
On the other hand, low-temperature image-fixing processes are desirable in view of minimizing energy consumption. Especially, in recent years, there exists the need for thorough energy-saving means, for example, by the terminating of electric supply except during use. As a result, such a fixing device should have a function to raise its temperature to an operating temperature in an instant. For that purpose, the heat capacity of the fixing device is desirably as small as possible. However in such a case, fluctuation in temperature of the fixing device often becomes greater than conventionally. For example, the overshoot temperature after starting electric supply becomes larger, and the decrease in temperature by the conveying of paper also becomes greater. Also if paper smaller in width than that of the fixing device is fed continuously, the difference between the temperatures of the paper-traveling area and the non-traveling area becomes enlarged. In particular, high-speed copying machines and printers when using the above function, often do not have a sufficiently large electric capacity, often resulting in the phenomena described above. Accordingly, there exists a strong need for a so-called wider-fixing-latitude electrophotographic toner that can be fixed at low temperature and does not cause offsetting until a higher temperature range is reached.
Use of a crystalline polycondensation resin or a crystalline condensation compound that exhibits a sharper melting behavior with respect to temperature as the binder resin for toner is known to be effective for lowering the fixing temperature of toner. However, because crystalline resins are more difficult to pulverize by the melt-kneading pulverization process they thus often cannot be used.
Polymerization of a polycondensation resin or production of a crystalline condensation compound normally also demands reaction conditions such as a high temperature of over 200° C., agitation under greater power, a highly reduced pressure, and a period of 10 hours or more, and therefore consumes a great amount of energy. Further, it often demands a large facility investment to ensure the durability of the reaction facilities.
When a toner is produce by the emulsion polymerization aggregation method as described above, after a crystalline polycondensation resin or crystalline condensation compound is produced by polymerization, it can be converted into a latex condition by emulsifying the resin or compound above in an aqueous medium, and coagulating it with a pigment, a wax, and the like, and melt-coalescing the resulting aggregate.
However, emulsification of a polycondensation resin or a crystalline condensation compound requires extremely inefficient and high-energy consumption processes to be used, for example, an emulsification process at a temperature of more than 100° C. to 150° C. under high-shear, or a process of dispersing in an aqueous medium a low-viscosity solution of the resin or compound which has been dissolved in a solvent, and then removing the solvent.
Because of the difficulty of avoiding the problem of hydrolysis during the emulsification in an aqueous medium, the generation of uncertainty factors in material design was also unavoidable.
Although these problems are significant when using crystalline resins, the same problems do not only occur when using crystalline resins but also when using noncrystalline resins.
There is a report that it is possible to perform polycondensation of polyester in an aqueous medium, which has been regarded as difficult (U.S. Pat. No. 4,355,154). There is also a report of polycondensation of polyester performed in an aqueous medium in the presence of a catalyst having a sulfonic acid group (U.S. Pat. No. 4,355,154).